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Derivative Financial Instruments - Summary of Outstanding Notional Balances and Fair Values of Outstanding Derivative Positions (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
IRLCs [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	$ 180,596	$ 202,906	$ 187,747
Asset Derivative Fair Value	1,645	4,618	296
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Outstanding Notional Balance	317,500	198,000	198,000
Asset Derivative Fair Value	$ 2,806	$ 0	0
Liability Derivative Fair Value			$ 0	$ 1,560	$ 3,200